Apple is the world's most valuable company, and it makes machines with screens. Comcast is America's largest cable provider, and it builds pipes that carry video to machines with screens. So the news that Apple and Comcast are talking about forming a special relationship might strike you as a written-in-the-stars marriage, like the varsity high school quarterback proposing to the head cheerleader.

It's also probably not happening. To explain why, let's start with a bit of history.

A fully integrated Apple television is the magical unicorn of consumer tech: Everybody can imagine what it looks like, even though it doesn't exist and perhaps never will.

Cupertino's TV strategy achieved mythic status after Steve Jobs' Rosebud comment to biographer Walter Isaacson, made shortly before he died, that he'd "finally cracked" the secret to disrupting the cloistered TV market. Precisely what Jobs had finally cracked was never clear, but that made it all the more tantalizing to Apple fanboys, who fleshed out his mysterious comment with their own fantasies. Gene Munster, the widely cited Apple analyst at Piper Jaffray & Co., envisioned a voice-activated "40 or 50-inch iPad" to debut "in late 2012 or early 2013."

Late 2012 and early 2013 came and went—so did late 2013 and early 2014—and still there is still no Apple television set. Instead, there is Apple TV, a modest (yet fairly popular) hockey puck device that slings iTunes, Netflix, Hulu and other online services onto the big screen.

Now Apple is reportedly talking to Comcast about building a new streaming-TV service with special access to the "last mile" of Comcast's cable pipes. Apple wants a dedicated lane of Comcast's cable highway, separated from the public Internet, to guarantee smoother streaming for its content. This is a bit like paying to drive in the HOV lane during rush hour. In exchange, Apple is also reportedly requesting a sliver of Comcast's cable fees.

It's fairly clear why this deal would be great for Apple—it would officially transform its TV "hobby" into a TV business. People once thought that Apple would build an actual TV, but actual TVs are a terrible, zero-profit product with a high-turnover rate. Others thought it would partner with media companies to offer a fresh take on the cable bundle, but media companies don't want to partner with the folks who destroyed the record industry by selling songs for $0.99. Therefore Apple's TV strategy must revolve around its hockey puck. Horace Dediu estimates that Apple has sold about 25 million of these guys. A deal with Comcast/TWC could easily double that figure.

But what exactly is in this for Comcast? The cable company would have to invest in new network equipment to make this partnership work. It would tempt net-neutrality restrictions by giving Apple preferential treatment along its pipes just as its Time Warner Cable acquisition faces accusations of a law-breaking monopoly. Plus, Comcast would have to give Apple a share of its pay-TV profits in exchange for popularizing a device that's partially seen as a replacement for pay-TV. Henry Blodget says there is no way this deal is going down. I say he's right.

Today, pay-TV is a mature business in moderate decline, and Apple TV is an immature business in steady ascent. Extrapolate those lines out far enough, and it might seem obvious to you that the future of video is a streaming set-top box that brings together live TV, Netflix, iTunes Video, and apps—and that Apple makes something very close to this already. But if Comcast is sure about this future, the company that owns the pipes doesn't need Apple TV to save itself yet. It needs a box of its own.